Linking historic downtown and the university, lively 4th Ave is a rare breed: a rough-around-the-edges, alt-flavored strip with not a single chain store or restaurant (except for Dairy Queen). The stretch between 9th St and University Blvd is lined with buzzy restaurants, coffeehouses, bars, bookstores, galleries, indie boutiques and vintage shops. It has its own traders' association along with events (see the website).
Under the overpass that crosses 4th Ave and Broadway is the Tucson Portrait Project, a wonderful public art project composed of thousands of locals' portraits.
Parking is free on weekends. The best time to visit 4th Ave is during the two annual street fairs held for three days in mid-December and in late March or early April. See the 4th Ave website for details.